Tunable high frequency electrodynamic driver



Dec. 16, 1969 J. F. MCCORMICK 3,484,730

TUNABLE HIGH FREQUENCY ELECTRODYNAMIC DRIVER Filed March 7, 1968 2Sheets-Sheet 1 INVENTOR. Josfifiv/ I. Ma tam/wk MJM Age/v7 Dec. 16, 1969.J F. M CORMICK 3,484,730

TUNABLE HIGH FREQUENCY ELECTRODYNAMIC DRIVER Filed March 7, 1968 2SheetsSheet 2 I v 5 '4 I INVENTOR. J056PH i Ma (@fiM/CK BY 4;; d gfgUnited States Patent 3,484,730 TUNABLE HIGH FREQUENCY ELECTRO- DYNAMICDRIVER Joseph F. McCormick, Hingham, Mass., assignor, by mesneassignments, to the United States of America as represented by theSecretary of the Navy Filed Mar. 7, 1968, Ser. No. 711,383 Int. Cl. HOlf7/08; H04r 9/00, 9/06 U.S. Cl. 335222 Claims ABSTRACT OF THE DISCLOSUREAn electrodynamie driver having a cylindrical movable coil assembly oflow mass radially supported by several equiangularly-spaced spring rodsgripped by adjustable split bushings releasably clamped by the rigidsupport portion of the driver assembly.

BACKGROUND OF THE INVENTION This invention pertains to the art ofelectrodynamic drivers.

SUMMARY OF THE INVENTION The invention concerns suspending the movingcoil assembly on several radial pring rods and split bushings on eachspring rod adjustable to establish the spring rod length for the desiredtuning and matching.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a plan view of anelectrodynamic driver, exclusive of holder and magnets;

FIG. 2 is a section taken on line 22 of FIG. 1, wherein part of the ringis broken away, and

FIG. 3 is a sectional view on an enlarged scale taken on line 3-3 ofFIG. 1.

Similar numerals refer to similar parts throughout the several views.

The disclosed embodiment of the invention includes a circular rigidsupport plate 10 having a central bore 12. The plate 10 is formed with acircular recess 14 in one face. The bottom of the recess is formed witha uniworm width circular channel 16 at the perimeter of the recess. Thesmaller diameter wall 18 of the recess is parallel to the axis of thebore. A ring 20 of lesser width than the width of channel 16 is seatedagainst the bottom of the channel 16 and against the smaller diameterwall 18 and is secured in place by press fit. A companion ring 22 ofessentially the same dimensions as the ring 20 is secured coaxially toring 20 in face-to-face relationship by means of eight machine screws24. The 0pposed faces of the rings are formed with matched V-shapedradial grooves 26 spaced ninety degrees apart around the rings. Twomachine screws 24 bracket each matched pair of grooves. Two radialgrooves 28 bracket a pair of the machine screws and serve as passagewaysfor connecting leads 30.

A moving coil assembly 32 is adjustably supported by the rings 20 and 22for axial oscillation. The coil assembly includes a thin-walled coilform 34 supporting a helically wound conductor 36. A spider 3 8 having acircular rim 40 of approximately the same outside diameter as the coilform is reduced in diameter at one end and press fitted into the coilform. The spider has four legs 42 that merge into axial junction 44 thatis threaded axially. Four thin spring rods 46 are secured in coplanarrelationship by being pressed into the legs 42 of the spider and projectradially outward of the spider by equal amounts. The distance fromtop-to-top of diametrically aligned rods is slightly less than thediameter of the recess 14- in plate 10. A split bushing 48, square incross- 3,484,730 Patented Dec. 16, 1969 p CC section, and wherein thesplit is a cut through one edge. and about 25% longer than the width ofthe rings, is mounted on each of the projections. The split bushings arenested in the V-shaped grooves with the cut in the bushing between therings to permit clamping. Each bushing is clamped and unclamped by thecorresponding pair of bracketing screws. Conducting leads 30 that extendthrough grooves 28 connected to the ends, not shown, of the helical coil36 and are cemented to the rim of the spider. The other ends of leads 30are connected to posts 50 that are secured in counterbores 52 in theplate.

The spacing between the outer perimeter of the rings and the circularwall of the recess is approximately equal to the spacing between theinner perimeter of the rings and the spider rim. The bushings 48 may beprovided with markings to facilitate adjustment of the four bushings fora desired frequency response of the moving coil assembly. When theclamping screws are loosened a thin tool can be used to adjust eachbushing radially.

One end of the helical coil is approximately coplanar with the recessedface of plate 10. Any constant field magnet means 54 conventional forinteraction with driver coils is secured against the face of the plate10 that is recessed. The magnets are sandwiched between the plate 10 anda holder 62.

A rod, not shown, is threaded into the center of the spider forconnection to a speaker cone, a low mass valve means of a hydroacousticamplifier, or other similar device.

This invention provides an adjustable low mass high modulus, high springrate assembly that permits matching and tuning. The spring rate and thusthe natural frequency of the assembly are tunable by adjustment of thesplit bushings.

It will be understood that various changes in details, materials, andarrangements of parts (and steps), which have been herein described andillustrated in order to explain the nature of the invention, may be madeby those skilled in the art within the principle and scope of theinvention as expressed in the appended claims.

Iclaim:

1. An electrodynamic driver comprising a hollow circular cylindricalcoil form carrying a helically wound conductor on its outer surface,

a circular member affixed coaxially to one end of said coil form,

a plurality of coplanar thin spring rods secured to said circular memberto extend radially outward therefrom and spaced equiangularly about theaxis coil form and circular member,

a split bushing carried by each spring rod and adjustable along thespring rod, and

means for clamping each bushing into gripping engagement with therespective spring rod and at a selected position along the rod, andoperable to selectively unclamp each bushing to permit independentadjustment of each bushing along the respective spring rod, forsuspending said coil form and circular member with equal lengths ofspring rod between the coil form and the split bushings.

2. An electrodynamic driver as defined in claim 1,

wherein said circular member includes an integral spider of severalequiangular spaced radial legs extending from the circular portion to anaxial junction of the legs.

3. An electrodynamic driver as defined in claim 2,

wherein said radial legs number four and said spring rods number fourand said spring rods are aligned with and are seated in said radiallegs.

4. An electrodynamic driver as defined in claim 3, means formed with acircular step onwhich one of wherein said rings is press fitted. 7

said split bushings are essentially square in cross-section and thesplit is radial and extends through one References Cited of the fouredges, 5 UNITED STATES PATENTS said means for clam in includes two rin sof e ual inside and outside di ameters and whici has s ub- 222106811/1940 Alons' stantially less radial thickness than the length f2263819 11/1941 Ray 335 222 the bushings, each ring having four radialequiangu- 2556816 6/1951 Lukacs 335-222 larly spaced V-shaped groovesfor seating the 'bushm G. HARRIS, Primary Examiner ings, and four pairsof clamping screws coupling the two rings, each pair of clamping screwsbracketing U.S. C1.X.R. aligned grooves in the two rings. 179-.1l5.5

5. An electrodynamic driver as defined in claim 4,

further including 7 15

